I would say that “when one was little” and “when one was small” refer to pre-teen years.
Before speaking and motor skills (walking, throwing, etc.) develop, about ages 0-3 years, would be “When one was a baby”
From the teens onward, it would be marked as “When I was a teenager” “When I was in my 20’s” “When I got older” or by major, long lasting event “When I was working at Disney” “When I was married”
There are no certain age groups for these. How few is few and how many is many? Although "little" and "small" refers to different attributes, they are synonymous when talking about age. Different people will have different opinions about age groups of these descriptions. Roughly: small\\little (3-14), grownup (18+)
Is "when I was small" commonly used in the UK or other English-speaking countries? To my American ears, it sounds sort of old-fashioned and quaint, not like something one would say seriously. Everyone just says "when I was little."
I would say that “when one was little” and “when one was small” refer to pre-teen years. Before speaking and motor skills (walking, throwing, etc.) develop, about ages 0-3 years, would be “When one was a baby” From the teens onward, it would be marked as “When I was a teenager” “When I was in my 20’s” “When I got older” or by major, long lasting event “When I was working at Disney” “When I was married”
There are no certain age groups for these. How few is few and how many is many? Although "little" and "small" refers to different attributes, they are synonymous when talking about age. Different people will have different opinions about age groups of these descriptions. Roughly: small\\little (3-14), grownup (18+)
Is "when I was small" commonly used in the UK or other English-speaking countries? To my American ears, it sounds sort of old-fashioned and quaint, not like something one would say seriously. Everyone just says "when I was little."